Poor neighbourhoods and slums in Bugama and Okrika in Nigeria, Freetown in Sierra Leone, Bathurst in the Gambia and Tanga in Tanzania, are especially vulnerable.
In such low-income urban centres, infrastructure is often non-existent or ill-maintained, according to a World Bank report, Sea level Rise and Storm Surges, while storm-water drainage infrastructure is often outdated and inadequate.
According to the Intergovernmental Panel on Climate Change (IPCC), a trend has emerged since the mid-1970s where storms tend to last longer and be more intense, with a strong correlation to the rise in tropical sea surface temperature.
In sub-Saharan Africa, storm surge zones are concentrated in Madagascar, Mauritania, Mozambique and Nigeria. These countries alone account for about half (53 percent) of the total increase in the region's surge zones resulting from sea level rise and intensified storms.
At least three cyclones struck Madagascar between January and April 2009, affecting thousands.
In Mozambique, one of the most vulnerable coastlines in Africa, 15 of the 56 tropical cyclones and tropical storms that entered the Mozambique Channel from 1980 to 2007 made landfall.
Tropical cyclones, also called typhoons and hurricanes, are powerful storms generated over tropical or sub-tropical waters whose impact includes extremely strong winds, torrential rains, high waves and damaging storm surges, leading to extensive flooding.
"Coastal flooding has started to be of concern in the last 10 to 15 years," Pedro Tomo, director of the Mozambique National Institute for Disaster Management, told IRIN. "Now, a few times each year, there are people who wake up in water."
In 50 years, Tomo said, some coastal towns will disappear if nothing is done - such as Nacala, Beira, Quelimane and Mahajanga.
Such a scenario would not just displace the population, but also damage economic infrastructure, said Michel Matera, programme manager, crisis prevention and recovery/environment, for the UN Development Programme in Mozambique.
At least 2.5 million people live in Mozambique's coastal areas, surviving on rain-fed farming and fishing. But migration to coastal towns is placing more people, infrastructure and services at risk, according to a study by the Mozambique institute.
"Models suggest that for the Indian Ocean there is an overall tendency toward decreasing frequency of tropical cyclones but increasing cyclone intensity," the report stated.
"More severe cyclones will pose the biggest threat to the [Mozambique] coast; beyond 2030, the accelerating sea level rise will present the greatest danger, especially when combined with high tides and storm surges," it added.
Researchers project a 3-5 percent increase in wind speed per degree Celsius increase of tropical sea surface temperatures. "The current understanding is that ocean warming plays a major role in intensified cyclone activity and heightened storm surges," it stated.
In a scenario of a high, non-linear sea-level rise due to polar ice melting, Beira "will be cut off from the interior and will likely become an island..."
Maputo's port, its rail links and oil facilities, which are on an estuary, are also subject to flooding.
Studies show that Mozambique, Ghana and Togo may lose more than 50 percent of their coastal gross domestic product (GDP), but losses would be highest in Nigeria (US$407.61 million).
Coastal agriculture, in terms of extent of croplands, will be affected 100 percent in Nigeria, 66.67 percent in Ghana, and 50 percent in Togo and Equatorial Guinea.
Mauritania is experiencing the impact of a changing climate exemplified by a steadily creeping desert and other extreme weather events. It is one of the countries likely to be worst affected by intensified storm surges.
"About every seven years, there are very high sea waves that sometimes flood up to 800m inshore," Mohamed Moulaye Ely, head of civil protection in Mauritania's Ministry of Interior, told IRIN. "In 1988, this happened during the day but in 2001 it was at night and most people were caught unawares."
Mauritania relies mainly on sand dunes as a natural barrier to control coastal flooding. The dunes cover a 5km stretch into the capital, Nouakchott.
"There isn't much prevention planning to deal with disasters here," he said. "We are like a fire brigade. We create a committee to respond when something happens."
Mauritania has a disaster management platform, but "...the political situation will be a major determiner of its success", he said. The military ousted former president Sidi Mohamed ould Cheikh Abdallahi in a 2008 coup.
Rising sea levels
Much of the land in and around Nigeria's commercial capital Lagos is less than 2m above sea level so it too is expected to be affected by rising sea levels.
In Cotonou, Benin, the continued advance of the sea, coastal erosion and the rise in sea levels are already threatening vulnerable communities and disrupting the least-protected sensitive ecosystems. Some roads, beaches and buildings have already been destroyed by the coastline's regression in the past 10 years.
Zanzibar is experiencing marine flooding, partly due to mangrove and coconut plantation felling, said Waride Jabu, director of the disaster management department. Erosion is also being experienced along the coastline, where an increase in building activity has been noted.
Coastal erosion is expected to threaten investment in beach resorts. This will arise from the gradual inundation of offshore islands and increased damage to the coral eco-systems, which will reduce their capacity to protect the coast.
Jabu said high tidal waves were increasing. "So far, no damage to infrastructure has been noted, but the sea seems to be slowly eating the shore." The Zanzibari disaster department was encouraging reforestation along the coastline.
In Eritrea, trees are being planted on the 1,100km coastline, said Solomon Haile, the director of the planning and statistics division in the Ministry of Agriculture. "The land is a bit elevated so we are not currently afraid of the sea rising," he added.
More than half the coastal population of Djibouti, Togo, Mozambique, Tanzania, and Sudan would be at risk from intensified storms and rising sea levels, experts say.
Counting the cost
According to the Mozambique study, the re-insurance industry has also recognised the need to increase the probability of tropical cyclones making landfall on vulnerable coasts in its risk calculations. "Risk carriers believe they cannot wait until science has provided answers to all the relevant questions, but must already make substantial upward adjustments to the cost of cover in such risk portfolios."
An average 78 million people worldwide are exposed each year to tropical cyclone wind hazard and another 1.6 million to storm surges. In terms of economic exposure, an annual average of $1,284 billion in GDP is exposed to tropical cyclones, according to the 2009 Global Assessment Report on Disaster Risk Reduction.
"Currently 10 percent of the world's total population (over 600 million people) and 13 percent of its urban population (over 360 million people) live on the 2 percent of the world's land area that is less than 10m above sea level, known as the Low Elevation Coastal Zone," it stated. "In Africa, 12 percent of the urban population lives in the LECZ."